rack and pinion

Here is a two-part Navy training film from 1953 that describes the inner workings of mechanical fire control computers. It covers seven mechanisms: shafts, gears, cams, differentials, component solvers, integrators, and multipliers, and does so in the well-executed fashion typical of the era.

Fire control systems depend on many factors that occur simultaneously, not the least of which are own ship’s speed and course, distance to a target, bearing, the target’s speed and course if not stationary, initial shell velocity, and wind speed and direction.

The mechanisms are introduced with a rack and pinion demonstration in two dimensions. Principally speaking, a shaft carries a value based on revolutions. From this, a system can be geared at different ratios.

Cams take this idea further, transferring a regular motion such as rotation to an irregular motion. They do so using a working surface as input and a follower as output. We are shown how cams change rotary motion to linear motion. While the simplest example is limited to a single revolution, additional revolutions can be obtained by extending the working surface. This is usually done with a ball in a groove.

This is a redesigned x-axis for [Peter Jansen’s] selective laser sintering rig. We looked in on his SLS project last month and since then he’s been refining the design. The new component uses a rack and pinion system, relying on some Kapton tape to reduce friction for a nice smooth slide. One stepper motor powers the laser-cut gear box with four gears interfacing the sled to the frame for stable and accurate motion. Now he’s just got to work out the math/physics that go into finding the optimal gear ratios as this prototype is just a rough guess. If you’ve got the skills to work it out please lend [Peter] a hand as we’re quite excited with where this is going.